Certainly not the first time I've mentioned the need to take a break and risking burnout but here is another note.
I once knew a pro triathlete who I came to coach who decided to skip recovery weeks and press on regardless of how tired he was. He was never the same again. Overtraining took a big bite out of his performance and he never fully recovered from it. Two years later he retired, prematurely, from the sport.
Professional athletes track so many stats on their health so that they know when they need a break. I'm a professional programmer but I don't track stats really on my mental health to see if I need a break from work.
I wonder how many programmers designers…leave the field early because they 'overtrained' and didn't take the breaks they needed to have a healthy long term career. I'd bet there are more of those than athletes that burned out.
The quote comes from Joe Friel, probably the voice on training for Triathlon or Cycling.